The present invention is related to the field of ion implanters used in semiconductor manufacturing.
An ion implanter generally includes a source that generates an ion beam including an ion species to be implanted along with a variety of undesirable ion species; an analyzer that employs a magnetic field to separate the trajectories of the various species and a resolving opening or slit through which the trajectory of the desired species passes; a module for adjusting the energy of the beam emanating from the resolving opening; and an end station in which the energy-adjusted beam interacts with wafers to effect the desired implantation.
Ion implanters can be classified according to the scanning technique that is employed to achieve relative motion between the beam and the wafers. In one class of implanters referred to herein as “beam scanning” implanters, one or more wafers being implanted are held stationary in the end station while the beam is scanned across each wafer's surface. The scanning can be achieved via magnetic or electrostatic interaction with the beam. In another class of implanters referred to herein as “wafer scanning” implanters, the beam remains substantially stationary and a wafer is mechanically moved across its path. In one sub-type of wafer scanning implanter, the cross section of the beam at the wafer is flat and broad, and therefore referred to as a “ribbon” beam, and the wafer is covered by the breadth of the beam as the wafer is scanned in the orthogonal direction (e.g., the beam may be flat in the horizontal plane and the wafer is scanned vertically). There are also implanters that employ a combination of beam scanning and wafer scanning. Each of the scanning techniques has its advantages and drawbacks, and each finds use in various semiconductor manufacturing operations.
Regardless of the scanning techniques they employ, ion implanters are generally susceptible to a class of operational problems in which the beam quality is suddenly degraded in the middle of an implantation operation, potentially rendering the wafer unusable. These problems are commonly referred to as “glitches” or “glitching” of the beam, and can be caused at various locations along the beam path. Ion implanters generally employ several electrodes along the beam path, which serve to either accelerate/decelerate the beam or to suppress spurious streams of electrons that are generated during operation. Generally, glitches occur across acceleration/deceleration gaps as well as suppression gaps. A glitch can be detected as a sharp change in the current from one of the power supplies for the electrodes. Because of the potential loss of an entire wafer, glitches are quite serious from a cost perspective, and thus measures are usually employed to both minimize the occurrence of such glitches and to recover from them if possible.
When a glitch is detected, it is ideally desired to immediately reduce the ion beam current to zero, thus terminating the implantation at a well-defined location on the wafer. Once the glitch condition has been removed, implantation ideally resumes at exactly the same location on the wafer, with ideally the same beam characteristics as existed when the glitch was detected. The goal is to achieve a uniform doping profile, and this can be achieved by controlling the beam current and/or the wafer scan speed (exposure time).
In implanters that employ beam scanning, it is generally possible to achieve glitch recovery that is reasonably close to this ideal. The circuitry that effects the normal scanning of the beam can be supplemented by glitch detection and recovery circuitry that (a) detects a glitch and immediately deflects the beam entirely away from the wafer, and (b) subsequently resumes implantation by rapidly moving the beam from off-wafer to the location at which implantation ended when the glitch was detected. Because of the fast beam deflection that can be achieved, the resulting implantation profile can be quite acceptable, and thus the wafer can be saved.